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Two immunoglobulin tandem proteins with a linking β-strand reveal unexpected differences in cooperativity and folding pathways.

Steward A, Chen Q, Chapman RI, Borgia MB, Rogers JM, Wojtala A, Wilmanns M, Clarke J - J. Mol. Biol. (2011)

Bottom Line: The structures of the tandem immunoglobulin (Ig) domain pairs A164-A165 and A168-A169, from the A-band of the giant muscle protein titin, reveal that they form tightly associated domain arrangements, connected by a continuous β-strand.We elucidate the folding and unfolding pathways of both tandem pairs and show that cooperativity in A164-A165 is a manifestation of the relative refolding and unfolding rate constants of each individual domain.We infer that the differences between the two tandem pairs result from a different pattern of interactions at the domain/domain interface.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.

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Structures of A164–A165 and A168–A169. (a) Ig tandem A164–A165 (violet; Protein Data Bank code: 3LCY) superimposed to Ig tandem A168–A169 (gray; Protein Data Bank code: 2J8H) showing connecting β-strand between each domain. Each domain has a single, buried Trp residue, shown, which is highly conserved in all Ig domains. These domains have been aligned using the N-terminal domain. Thus, the Trp residue in A164 is superimposed on that of A168. Domains A165 and A169 do not superimpose well, reflecting the different rotation of the domains in the tandem pairs. (b) The domain interface of A164–A165: the N-terminal domain is shown in red, the C-terminal domain is in blue, the connecting β-strand is in cyan, the loops are in light green, and the helical residues are in yellow. Side chains of buried residues Q72, E75, and R130 are involved in a network of interdomain interactions, both hydrogen bonds (blue) and a salt bridge (red). (c) The domain interface of A168–A169: presented in the same way as in (b). There is a surface-exposed salt bridge between D69 and K129 but no other side-chain-mediated hydrogen bonds.
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f0005: Structures of A164–A165 and A168–A169. (a) Ig tandem A164–A165 (violet; Protein Data Bank code: 3LCY) superimposed to Ig tandem A168–A169 (gray; Protein Data Bank code: 2J8H) showing connecting β-strand between each domain. Each domain has a single, buried Trp residue, shown, which is highly conserved in all Ig domains. These domains have been aligned using the N-terminal domain. Thus, the Trp residue in A164 is superimposed on that of A168. Domains A165 and A169 do not superimpose well, reflecting the different rotation of the domains in the tandem pairs. (b) The domain interface of A164–A165: the N-terminal domain is shown in red, the C-terminal domain is in blue, the connecting β-strand is in cyan, the loops are in light green, and the helical residues are in yellow. Side chains of buried residues Q72, E75, and R130 are involved in a network of interdomain interactions, both hydrogen bonds (blue) and a salt bridge (red). (c) The domain interface of A168–A169: presented in the same way as in (b). There is a surface-exposed salt bridge between D69 and K129 but no other side-chain-mediated hydrogen bonds.

Mentions: The A-band of titin is made up of Ig and FNIII domains, which are mostly arranged in repeating patterns.17,18 A conformational characterization of three FNIII tandems from the A-band shows that these contrast markedly with Ig tandems from the elastic I-band: the FNIII interfaces were found to be conformationally well defined, exhibit limited dynamics, and are largely conserved.19 The Ig I-set domains A164, A165, A168, and A169 are located in the A-band segment of titin, N-terminal to the titin kinase domain and M-band.20,21 The linker between the two domains is one residue shorter than that between Ig domains in the I-band of titin. Importantly, in the tandem Ig pairs A164–A165 and A168–A169, the C-terminal G-strands of A164 and A168 are connected via a continuous β-strand with the N-terminal A-strands of A165 and A169, respectively (Fig. 1a). Here, we investigate the hypothesis that a continuous β-strand can impart cooperative folding between adjacent Ig domains, as a continuous α-helix does in spectrin R1617.22


Two immunoglobulin tandem proteins with a linking β-strand reveal unexpected differences in cooperativity and folding pathways.

Steward A, Chen Q, Chapman RI, Borgia MB, Rogers JM, Wojtala A, Wilmanns M, Clarke J - J. Mol. Biol. (2011)

Structures of A164–A165 and A168–A169. (a) Ig tandem A164–A165 (violet; Protein Data Bank code: 3LCY) superimposed to Ig tandem A168–A169 (gray; Protein Data Bank code: 2J8H) showing connecting β-strand between each domain. Each domain has a single, buried Trp residue, shown, which is highly conserved in all Ig domains. These domains have been aligned using the N-terminal domain. Thus, the Trp residue in A164 is superimposed on that of A168. Domains A165 and A169 do not superimpose well, reflecting the different rotation of the domains in the tandem pairs. (b) The domain interface of A164–A165: the N-terminal domain is shown in red, the C-terminal domain is in blue, the connecting β-strand is in cyan, the loops are in light green, and the helical residues are in yellow. Side chains of buried residues Q72, E75, and R130 are involved in a network of interdomain interactions, both hydrogen bonds (blue) and a salt bridge (red). (c) The domain interface of A168–A169: presented in the same way as in (b). There is a surface-exposed salt bridge between D69 and K129 but no other side-chain-mediated hydrogen bonds.
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Related In: Results  -  Collection

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f0005: Structures of A164–A165 and A168–A169. (a) Ig tandem A164–A165 (violet; Protein Data Bank code: 3LCY) superimposed to Ig tandem A168–A169 (gray; Protein Data Bank code: 2J8H) showing connecting β-strand between each domain. Each domain has a single, buried Trp residue, shown, which is highly conserved in all Ig domains. These domains have been aligned using the N-terminal domain. Thus, the Trp residue in A164 is superimposed on that of A168. Domains A165 and A169 do not superimpose well, reflecting the different rotation of the domains in the tandem pairs. (b) The domain interface of A164–A165: the N-terminal domain is shown in red, the C-terminal domain is in blue, the connecting β-strand is in cyan, the loops are in light green, and the helical residues are in yellow. Side chains of buried residues Q72, E75, and R130 are involved in a network of interdomain interactions, both hydrogen bonds (blue) and a salt bridge (red). (c) The domain interface of A168–A169: presented in the same way as in (b). There is a surface-exposed salt bridge between D69 and K129 but no other side-chain-mediated hydrogen bonds.
Mentions: The A-band of titin is made up of Ig and FNIII domains, which are mostly arranged in repeating patterns.17,18 A conformational characterization of three FNIII tandems from the A-band shows that these contrast markedly with Ig tandems from the elastic I-band: the FNIII interfaces were found to be conformationally well defined, exhibit limited dynamics, and are largely conserved.19 The Ig I-set domains A164, A165, A168, and A169 are located in the A-band segment of titin, N-terminal to the titin kinase domain and M-band.20,21 The linker between the two domains is one residue shorter than that between Ig domains in the I-band of titin. Importantly, in the tandem Ig pairs A164–A165 and A168–A169, the C-terminal G-strands of A164 and A168 are connected via a continuous β-strand with the N-terminal A-strands of A165 and A169, respectively (Fig. 1a). Here, we investigate the hypothesis that a continuous β-strand can impart cooperative folding between adjacent Ig domains, as a continuous α-helix does in spectrin R1617.22

Bottom Line: The structures of the tandem immunoglobulin (Ig) domain pairs A164-A165 and A168-A169, from the A-band of the giant muscle protein titin, reveal that they form tightly associated domain arrangements, connected by a continuous β-strand.We elucidate the folding and unfolding pathways of both tandem pairs and show that cooperativity in A164-A165 is a manifestation of the relative refolding and unfolding rate constants of each individual domain.We infer that the differences between the two tandem pairs result from a different pattern of interactions at the domain/domain interface.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.

Show MeSH